A vertical cavity surface emitting laser (VCSEL) is a laser device formed from an optically active semiconductor layer (e.g., AlInGaAs or InGaAsP) that is sandwiched between a pair of highly reflective mirror stacks, which may be formed from layers of metallic material, dielectric material or epitaxially-grown semiconductor material. Typically, one of the mirror stacks is made less reflective than the other so that a portion of the coherent light that builds in a resonating cavity formed between the mirror stacks may be emitted from the device. Typically, a VCSEL emits laser light from the top or bottom surface of the resonating cavity with a relatively small beam divergence. VCSELs may be arranged in singlets, one-dimensional or two-dimensional arrays, tested on wafer, and incorporated easily into an optical transceiver module and coupled to a fiber optic cable.
In general, a VCSEL may be characterized as a gain-guided VCSEL or an index-guided VCSEL. An implant VCSEL is the most common commercially available gain-guided VCSEL. An implant VCSEL includes one or more high resistance implant regions for current confinement and parasitic reduction. An oxide VCSEL, on the other hand, is the most common index-guided (laterally and vertically) VCSEL. An oxide VCSEL includes oxide layers (and possibly implant regions) for both current and optical confinement.
VCSELs and VCSEL arrays have been successfully developed for single-mode operation and multi-mode operation at a variety of different wavelengths (e.g., 650 nm, 850 nm, 980 nm, 1300 nm and 1550 nm). The commercial success of VCSEL technology, however, will depend in large part upon development of VCSEL structures that are characterized by high performance and high reliability.
Techniques have been proposed for improving the performance and reliability of a wide variety of different semiconductor laser devices, including VCSELs and edge-emitting lasers.
For example, U.S. Pat. No. 5,838,705 discloses VCSEL devices (i.e., a non-planar ridge VCSEL and a planar implant VCSEL) that include one or more defect inhibition layers that are positioned in a respective one of two cladding regions that are formed on opposite sides of an active area. According to the '705 patent, the defect inhibition layers may be disposed anywhere outside of the active area. However, the only preferred locations for the defect inhibition layers are in close proximity and on either side of the active area to provide a barrier that does not allow defects formed outside of the active area to pass through and into the active area. The defect inhibition layers are formed from an indium-containing material that induces strain in the VCSEL device. The strain is believed to either prohibit movement of defects to the active area or attract and, subsequently, trap defects in the defect inhibition layers.
U.S. Pat. No. 4,984,242 discloses a GaAs/AlGaAs edge-emitting laser that includes at least one cladding layer that includes indium. According to the '242 patent, the indium creates a local strain field that is sufficient to reduce and effectively stop defect migration through the cladding layer. The indium-containing strain layer may be spaced apart from the active region or may be positioned adjacent to the active region. Indium-containing layers may be added to the active region barrier layers to improve the performance of the edge-emitting laser. In one embodiment, a uniform doping of indium is provided throughout the edge-emitting laser heterostructure to impede the growth and migration of defects in the crystal lattice. Another embodiment includes indium in a cap layer to reduce the surface work function and, thereby, reduce the contact resistance of an overlying metallization layer. The '242 patent does not teach or suggest the use of indium in a VCSEL, nor does it teach or suggest how indium might be translated to a VCSEL structure.